Cross-hole Seismic Travel Time Tomography Applied before Tunnel Excavation by using TBM

Sule, Mohammad Rachmat; Octova, Adree

doi:10.3997/2214-4609.20143343

Cited by 1 publication

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“…The difference between the observed arrival time from acquisition and the calculated arrival time will be used to invert the model by updating the velocity in iterative manner (Hole et.al, 1995). The inversion procedure is the regularisation scheme (Sule, 2012), which minimizes an objective function that includes norms that measure model roughness and data misfit. The objective function 𝜙𝜙 minimized at each iteration is…”

Section: Methodsmentioning

confidence: 99%

Application of Cross-hole Seismic Tomography to Inferred Cavities Condition.

Fatkhan,

Ryannugroho,

Lawrens

et al. 2023

IOP Conf. Ser.: Earth Environ. Sci.

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The construction of the Rajamandala hydroelectric power plant civil works has experienced critical problems that arise in the implementation process, with the occurrence of cracks cavities conditions in the headrace tunnel locations. We applied the cross-hole seismic tomography to detect important heterogeneities and mechanical proprieties of the formations between two boreholes in this case inferred cracks cavities condition. The seismic source is inside the borehole “a sparker” and the receivers “hydrophones” are in an adjacent one, the sparker is lowered into the borehole one step at the time. Seismic waves, propagating in the tunnel wall rock, spread widely, and are reflected and refracted when encountering interfaces between rocks with different acoustic impedances. Reflected waves returning to the receivers are recorded. After the processing of the first arrivals of the P waves we obtain a cross section of the seismic velocities in between the two wellbores. With the cross-hole seismic tomography, the basis could be provided to the tunnel construction and parameter adjustments to guarantee the construction safety. Our result shown that there is a weak zone above the tunnel with low Vp zone (~1.2 km/s) may be related to weak zone (may be fracture, unconsolidated rock, and fluid-filled rock or landslide caving). Checker-board resolution test is also conducted to determine the tomogram areas that are reliable to be interpreted. Our challenges are we have poor resolution due to not enough raypath. The Cross-hole seismic tomography can effectively and safely guide the excavation of the tunnel section working surface in combination with reconstructed images and excavation technology.

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Section: Methodsmentioning

confidence: 99%